The present invention relates to a process for brake pressure restoration in a motor vehicle with an anti-lock brake system.
Anti-lock brake systems in motor vehicles function, as is known, in such manner that the rotational speeds of the wheels are sensed by means of rpm sensors and the brake pressure of a wheel is quickly lowered if it is found that it tends to lock. As a result, the wheel is able to run up again. The rapid lowering of brake pressure is followed as a rule by a brake pressure maintenance phase. Following this, the brake pressure is increased once more. This generally occurs in two phases. In a first phase, the brake pressure is increased as rapidly as possible until it is close to the previous locking or deregulating pressure (see DE-OS 21 64 094/U.S. Pat. No. 3,833,094). This rapid brake pressure increase phase serves to go as quickly as possible through the hysteresis of the wheel brakes. Following the phase of rapid brake pressure increase, a slow pressure increase phase follows as a rule and serves to approach the new locking pressure slowly. As soon as the new locking pressure is attained, a new pressure regulating cycle with rapid lowering of the brake pressure from the deregulating pressure to the holding pressure follows.
It is also already known (see DE-OS 19 44 610) to use the level of the last locking pressure as a control for aerating the brakes following a lowering of braking pressure. For this purpose, compressed air is conveyed through an adjustable choke which is adjusted by the last locking pressure during the restoration of the brake pressure. As a result, the increase in brake pressure is attenuated, and this attenuation is slight at high locking pressure and substantial at a low locking pressure.
The known types of controls which are applied during the restoration of brake pressure are designed first of all to shorten the braking distance, in that the braking pressure is held for an extended period of time just below the locking pressure, and secondly to increase comfort, in that the ABS regulating cycles are achieved with the smallest possible fluctuations of the mean brake pressure.
It is the object of the present invention to provide an even more sensitive control, which is better adapted to the road conditions during the brake pressure restoration phase during a brake regulating cycle of an anti-lock brake system (ABS), and thereby to further increase comfort during the brake regulating cycle.